Polyvinyl chloride foam plastic foaming method
DATE：2021/11/19 8:47:42 / READ： / SOURCE：This station
Polyvinyl chloride foam plastic foaming method
Polyvinyl chloride resin is the main raw material for the production of polyethylene foam. The foam produced can be divided into high-quality polyhydrogen vinyl foam and rigid vinyl chloride foam: the main quality poly-hydrogen vinyl foam can be divided according to the foaming ratio. For high foaming and low foaming.
Method for foaming high-quality vinyl chloride foam
High-quality hydrogen ethyl foam can be made by physical foaming method with dissolved gas as the foaming agent and chemical foaming method with adding thermal decomposition foaming agent
1. Physical anti-bubble method
Because ethylene itself does not dissolve inert gas, a large amount of plasticizer that can decompose gas must be used to prepare polyvinyl chloride paste or solution. The molding method can be divided into two types: the case number method and the continuous method.
(1) In the batch method, a certain amount of polyvinyl chloride paste is added to the high pressure, and high pressure inert gas (such as carbon dioxide) is introduced under stirring. When the pressure is stabilized at 20-30 atmospheres (1 atmosphere=101325Pa), the inflated polyvinyl chloride is injected into the mold from the nozzle at the bottom of the kettle, and then sent to the oven at 110-135℃ as soon as possible. After the plastic is melted, it is cooled and removed. The mold obtains the foamed plastic product. The process of this method is relatively simple.
The mold used can be made of cardboard, aluminum or other metals. The open-cell foam plastic is made by the mouth mold, and the closed-cell foam plastic is made by the closed mold. The gelation and melting of foamed plastics can be carried out in a drying chamber, or high-frequency heating can be used, which can greatly shorten the heating time. For example, for a foamed plastic sheet with a thickness of 75mm, it takes only 4min to use high-frequency heating, but it takes 3h to heat it in a general oven.
(2) Continuous method The production process flow of the continuous method is shown in Figure 7-1. The polyoxyethylene paste is continuously sent to a special mixer with a pump from the storage grains and mixed with carbon dioxide at 20-25 atmospheres (1 atmosphere=101325Pa). The mixer is equipped with a temperature control device to ensure uniform mixing. The mixed aerated material is sprayed quantitatively to the conveyor belt from the nozzle of the mixer, and is scraped flat with a scraper, and then gelled and melted by high-frequency heating. The melting temperature is controlled at about 150°C. The melted and plasticized material is cooled and sliced to obtain an open-cell foam with a certain thickness.
The viscosity of the PVC paste used in the production of this method should be appropriate, and the gelling temperature range should be medium, so that the gas will easily form bubbles in the plastic paste. If the viscosity of the plastic paste is too large and the gelling temperature range is small, it will not easily form bubbles; on the contrary, if the viscosity is too small, the gas will easily escape. For this reason, the rheological behavior of the plastic paste is required to be a pseudoplastic fluid, so that the plastic paste can dissolve enough gas to become a stable foam system and maintain its stable state until the gelation process. The density of foam products mainly depends on the pressure and solubility of the inert gas and the plasticizer content in the plastic paste. The plasticizer content is low, the inert gas pressure is low, and the dissolved amount is small, and the density of the foam is high.
Author：admin